Feeding suppression in the tobacco hornworm, Manduca sexta: costs and benefits to the parasitic wasp Cotesia congregata

Abstract

While the larvae of the parasitic wasp Cotesia congregata developed inside the tobacco hornworm, Manduca sexta, the host's behaviour was similar to that of unparasitized M. sexta. However, once the wasps had exited the host to spin their cocoons, M. sexta stopped feeding. Unparasitized M. sexta ate C. congregata cocoons, which suggests that cessation of feeding by parasitized M. sexta prevented them from consuming the wasps' cocoons. However, suppression of host feeding might be expected to lead to increased host mortality. Host mortality decreased wasp survival. Few cocoons (18%, n = 43) attached to dead hosts produced adult wasps, while 90% of cocoons on live hosts successfully produced adults (n = 20). In the field there was no significant increase in host mortality during wasp pupal development. Cotesia congregata appeared to benefit from the lack of feeding by M. sexta without incurring the increase in mortality that would result if the host died from its lack of feeding. Although cocoons that were detached from the host were more successful (55% produced adults, n = 20) than those attached to a dead host, there was no evidence that wasps emerging from dying M. sexta were more likely to form cocoons away from the host.